Electric organ



Sept. 2, 1947. P. H. FROHMAN 2,426,605

ELECTRIC ORGAN Filed July 21, 1942 Patented Sept 2, 1947 UNITED STATES PATENT OFFICE 19 Claims.

This invention relates to electrical musical instruments and more particularly to electric organs in which reeds are utilized to produce electrical oscillations or alternating currents which are then translated into audible sounds closely analogous to those produced by organ pipes.

It has been found that the characteristic cutting sound peculiar to the free reeds used in a reed organ is due to air vibrations of high fre quency caused by the manner in which the reeds out the air rather than to the air vibrations produced by the mechanical vibrations of the reeds themselves.

The nasal quality of these high frequencies is partly due to the relative amplitudes of frequencies such as the 3rd, 5th, 7th and 9th harmonics, etc., that are not even multiples of the fundamental and deficiency in the 2nd and 4th harmonies that are even multiples of the fundamental. When these air vibrations of high frequencies are eliminated, the resulting sound wave is a more smooth and pleasing toneresembling that produced by an organ pipe. In reeds tuned to high frequencies this nasal or cutting sound is less apparent because the vibrations which cause it are of small energy as compared to the fundamental tone and because they approach the frequency limit of audible sounds. However, in reeds tuned to lower frequencies these higher harmonics become increasingly audible and in lower treble, tenor and bass ranges, they com prise a relatively large proportion of the total sound energy as compared with the fundamental tone.

Thus the musical defect of the reed organ is lack of fundamental tone, especially in thebass, tenor and lower treble, resulting from too large a proportion of sound energy in certain harmonies of high frequency. This results in the thin, nasal sound which is characteristic of the reed organ and distinguishes it from the full, round tone of the fundamental stops of the pipe organ. It has been proposed heretofore to eliminate the nasal qualities of reed tone in electric organs by the use of electrostatic or electromagnetic pick-ups associated directly with the reeds, and in some cases the tonal results so obtained have been closely analogous to those produced by organ pipes. Efforts to attain this end with microphonic pick-ups, on the other hand, have required complex and expensive systems with a plurality of microphones, filters and switching devices, or have merely produced the amplied tones of a reed organ which do not resemble the tones of organ pipes.

One of the objects of the present invention is to provide an electric organ which produces organ tones from reeds but With simple microphonic pick-up and amplification whereby the complex and expensive systems heretofore proposed are avoided and a simple, inexpensive organ is produced which nevertheless produces very satisfactory tonal results.

Another object is to provide novel apparatus for suppressing or eliminating the undesirable high frequency harmonics produced by reeds, especially those tuned to lower frequencies or pitch, While maintaining the proper balance of fundamental energy throughout the scale.

Another object is to suppress or eliminate the undesirable high frequency harmonics produced by reeds, especially those tuned to lower frequencies or pitch, by acoustical means operative prior to the time when the reed vibrations are picked up microphonically and translated into electric currents.

A further object is to provide a novel tone generator for electric organs in Which a large proportion of the energy of the harmonics generated by the vibrating reeds, particularly in the bass and tenor ranges, is absorbed acoustically from the sound Waves within the generator.

A still further object is to provide electrical amplifying apparatus, in combination with a tone generator of the above type, whereby the relative energy of fundamentals and harmonics of varying frequencies can be adjusted to provide a desired balance of tone volume throughout the scale and to modify tonal qualities so that a number of varieties of pipe-like tones can be produced from a single set of reeds.

One form of tone generator embodying the invention is illustrated in the accompanying drawings, together with different forms of associated amplifying apparatus, but it is to be expressly understood that the drawings are for purposes of illustration only and are not to be construed as a definition of the limits of the invention, reference being had to the appended claims for this purpose.

in the drawings,

Fig. 1 is a sectional plan and wiring diagram of one embodiment of the invention;

Fig. 2 is a vertical transverse section of the tone generator of Fig. 1;

Fig. 3 is a vertical longitudinal section of Vthe tone generator of Fig. l; and

Fig. 4 shows the tone generator' of Figs. l, 2 and 3 diagrammatically together with a wiring diagram of another form of electrical reproduction apparatus.

Broadly speaking, if the tone generator is arranged so that the sound waves must travel a substantial distance from the reeds to the microphone, there is an accompanying loss of energy, but on the other hand, the loss of energy is relatively greater in the case of the undesirable, high frequency harmonics than in the case of the fundamental frequencies. Thus the effect is to reduce the amplitudes of the undesirable harmonics relative to the fundamental frequency and to suppress or eliminate the undesirable thin, nasal quality characteristic of normal reed tones, while the somewhat weakened fundamentals which reach the microphone can be picked up and amplified to produce substantially true organ tones. As described, hereinafter, the extent to which this effect is produced is preferably increased by the use of baffles to lengthen the path of travel of the sound waves, or by the use of acoustical filters, so that the size of the tone generator is not unduly enlarged.

As noted above, the presence of these high frequency harmonics is not so objectionable in the treble range, and the importance of their suppression or elimination becomes greater as the tuned frequency or pitch of the reeds decreases. Preferably, therefore, the reeds are arranged more or less in line and in order of increasing pitch toward the microphone, so that the travel of the sound waves becomes longer and longer and the above eiiect is correspondingly increased for reeds of lower and lower pitch. At the microphone, however, the energy of the lower fundamental frequencies is reduced relative to that of the high fundamental frequencies, and hence I provide amplifying means in which the desired proportion or balance of energy throughout the scale can be restored, as by over-amplifying the low frequencies or by under-amplifying the high frequencies. Thus a balanced tone regulation and a balanced quality of voicing are obtained throughout the entire scale.

The application of the foregoing principles is illustrated by the tone generator and amplifying and reproducing systems shown in the drawings. The reeds, which may be similar to the reeds of a reed organ, are mounted in any suitable manner on an organ chest I and are actuated either by vacuum or by air pressure. Any desired number and arrangement of reeds may be adopted, two sets of reeds being shown and reeds 2 being tuned to 8 pitch while reeds 3 are tuned to 4 pitch.

The reeds of 4 pitch are voiced softer than the reeds of 8 pitch, but louder than the harmonics of the 8 reeds that are of nasal quality. The purpose of this Second set is to build up the octave or 2nd harmonic and reduce the nasal character of tone at its source, before all of the harmonics are further reduced by acoustical and electrical means. A marked second harmonic is one of the characteristics of pipe tones, while in reeds the 3rd harmonic is more prominent. The reeds are preferably enclosed by a soundproofed box 4 mounted on the chest I, and the whole may be further encased by insulated box 5. Each reed is tuned to a note in the equally tempered scale as in an organ, the reeds to the left being the bass reeds, the scale ascending to the right, and the top treble reeds being at the right end of the box nearest to a suitable microphone 6.

The reeds 2 and 3 may suitably be mounted on plates I which are inserted in slots in the box 4 and have openings B registering with openings 9 in the top of the chest I. The registered openings 8, 9 may be opened and closed in any suitable manner as by valves shown diagrammatically at I), the valves being operated by key action either mechanically, pneumatically or electropneumatically or electrically as in reed organs or as in a pipe organ.

In the form shown, the length of the path traveled by the sound waves to the microphone 6 is increased by partitions or baffles II between each pair of reeds 2, 3, said partitions having openings I2 which are staggered as shown in Figs. 1 and 2 so that the sound waves follow a sinuous path. If desired, the openings I2 may be covered with acoustical filter material which suppresses the undesirable, high frequency harmonics, such as silk fabric indicated at I3 in Fig. 2. In some cases the partitions I I may be made of such material, in which event the openings I2 may be unnecessary. For a purpose described hereinafter a partition I4 adjacent the top of box 4 may also be provided with openings to permit sound waves from the reeds to reach the microphone 6 directly, which openings may be controlled by a hinged lid such as used in stops for some forms of reed organ or by slide valves such as used in old pipe organs and accordions. In the form shown, a slide I5 is actuated by a rod IB and lever I1 to open or close the openings in partition I4.

The microphone 6, of appropriate type and frequency response, is connected by shielded and grounded cables I8 with a suitable audio frequency amplifier I9. In the system shown in Fig. 1, a condenser 20 and variable resistance 2I are connected across the output of the amplifier. A condenser 22 is connected in series with a variable resistance volume control 23 and a suitable loud speaker 24. The condenser 22 may be bypassed by closing a switch 25, and a second switch 26 may be closed to place a condenser 21 in parallel with the loud speaker. The capacity of the condensers will depend upon the impedance of the amplifier output transformer and the speaker and on the tonal results desired. The volume control 23 of the loud speaker may be operated by a swell pedal at organ console, and the switches 25 and 26, etc., by stop knobs or tilting tablets at the console.

When a bass reed sounds, the slide I5 being closed, the sound travels through the several chambers of the box 4 before reaching microphone 6. Due to the distance traversed and the form of the acoustical baille, as explained above, the energy of the high frequency harmonics is materially reduced by the time the sound waves reach the microphone, but the amplitude of the fundamental tone is not reduced to the same degree. The sound which reaches the microphone is therefore of much smoother quality than the original tone of the reed. When notes nearer the treble end are sounded, the distance traversed and number of baiiles encountered are less so that there is less loss of energy of harmonics of high frequency relative to the fundamental frequencies, but as noted above these higher harmonics are less noticeable in the treble range and less correction is needed.

On the other hand, there is also more loss of energy of the fundamental frequency in the lower ranges than in the treble range. Therefore in playing a scale it would be found that the sounds reaching the microphone would be soft and smooth in the bass and progressively louder and more harmonic as they ascend the scale. If these sounds were amplified and reproduced without correction, the result would be tones which were practically free from the undesired harmonics of reeds, but the instrument would be top heavy; that is to say, the bass would be weak and the top treble loud as com` pared with the middle of the scale. `To restore the proper proportion and balance of energy throughout the scale, the amplitudes of the notes of higher frequency are suitably reduced rela,- tive to the notes of lower frequency, preferably by increasing the capacity of the condenser 23 of the tone control of the amplifier and by the adjustment of the variable resistor 2|.

Thus the out-put of amplifier. I9, when din rectly connected to the loud speaker 24 which is of average frequency response, produces sounds of pipe-like quality, with the harmonics of string or` diapason character rather than ofthe cutting nasal quality of reed tones. 'I'he additional controls shown in Fig. 1 enable varying `tonal effects to be obtained from the single set of reeds. When switches 25 and 26 are open the condenser 22 is in series with the loud speaker 24 `so that thevoltages of-lower frequencies are reduced. The resulting sounds therefore have a relatively weak fundamental and consequently are of a thin string-like quality. If switch 25 is closed the fundamentals are increased and the resulting tones resemble those of an open diapason. If switch 26 is closed the condenser 21 tends to by-pass or short circuit rthe frequencies of the harmonics only and the resulting Voltage wave passing through the voice coils of the loud spaker is practically a sine wave and produces tones of pure, flute-like quality.

Ifv in addition to producing tones of smooth string, diapason and flute qualities, it is desired to produce reed tones, then slide I5 may be drawnv thereby permitting the sounds of the reeds to reach the microphone without the intervention of the acoustical baiiies. If switches 25 and 26 are open, the reed tones'will be of a thin and cutting character. With switch 25 closed the reed tone will becomemore full and with switch 26 closed it will be of distinctly smooth quality. The harmonic characteristics of the tone may be further varied by adjustment of the tone control of the amplifier as well as by the position of the slide valve I5.

Fig. 4 shows separate loud speakers 28, 29 and 30 of varying frequency response which are connected with separate out-put transformers 3l, 32 and 33 respectively. The speaker 28 is in series with a condenser 34 and produces a string tone. The speaker 29 with no condensers gives a diapason tone and the speaker 30 in parallel with a condenser 35 gives a flute-like tone. Each speaker may be controlled individually by a stop switch or a variable resistor at the organ console,V as shown at 36, 31 and 38, so that various combinations of tones may be obtained, and a further volume control 39 may be provided which corresponds to the variable resistance 23 of Fig. 1. As the volume of each speaker may be varied, it is possible to obtain a much greater number of combination tone colors than on a pipe organ with the same number of stops. By adding the harmonics obtained directly from the reeds to those which are modified by the baille box, it is possible to produce a very large number of gradations of tone from one set of reeds.

It will be understood that the values yof the condensers referred to above will vary depending on factors such as the progressive increase in energy from base to treble of the sound waves reaching the microphone, the effectiveness of the baffles in progressive reduction of undesired harmonics from treble to bass, the harmonic response and characteristics of the microphone, the characteristics of the amplifier and loud speakers, etc. The condenser 29 may be the condenser of the usual tone control incorporated in the amplifier. By way of example as to the other condensers, in an organ using an R. C. A. Aerodynamic microphone and a 20 watt R. C. A. amplifier with the wires to the loud speakers connected to the 250 ohm tops, good results were obtained with the following values: 0.25 mfd. for condenser 22 and 2.00 mid. for condenser 21 in Fig. 1; 0.125 to 0.25 mfd. for condenser 34 and 2.0 to 4.0 mid. for condenser 35 in Fig. 4.

The second set'of reeds 3 may be used as a separate 4' stop, as an octave, or as a 4 flute, as well as to increase the second harmonic which is required for a diapason tone or a string tone but is not desired for certain qualities of flute tones.

An electric organ of the type described above is thus capable of producing the four essential qualities of organ tone with one tone generator and one loud speaker as, in the embodiment shown in Figs. 1-3, or it may have a separate tone generator for each stop, or where maximum volume is desired it may have a separate tone generator and separate amplifier and loud speaker for each of the main families of organ tone. For example, for a two manual organ of average volume and Variety three tone generators might be used, one for the great organ, one for the swell organ and one for the pedal organ. When a vox celeste stop is desired it is necessary to have an additional set of reeds tuned to beat with the 8 stops.

In ,practice it is not necessary in all cases to have a baffle partition for each reed. If the tone of the reeds is first smoothed by properly proportioned resonating chambers, fewer baflles are required; for example, one partition for each octave may be sufficient. The number of partitions, the size of the holes therein, etc., are matters of the smoothness of tone desired and depend as well on the characteristics of the microphone and amplifier, the capacities of the condensers, and the frequency response of the loud speakers. Thus care in design and matching of each stage of the production, modification, translation and reproduction of the tones is desirable for best results. However, the principles involved are apparent from the foregoing description and it is evident that an organ built on these principles has great electrical simplicity but yet provides a wide variety of tonal effects and compares favorably with other electric organs `which produce pipe-like qualities of tone by means of electrostatic, electromagnetic or microphonic methods.

It is to be expressly understood thatthe embodiments of the invention described with particularity above and illustrated in the drawings are for purposes of illustration only, and that various changes in the form, details of construction and arrangement of the parts will now be apparent to those skilled in the art,without departing from the spirit of the invention. It will also be understood that the acoustical baffle or filter means may be used in a reed organ of the usual type, if desired, in which case the bass and tenor would be of smoother quality than the treble in- 7 stead of being more rough as is usually the case. Reference should therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound Waves from said reeds to said outlet is longer for low frequencies than for high frequencies, and means interposed in said path of travel for progressively reducing the energy of high frequency harmonics.

2. An organ tone generator comprising a casingl having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for higher frequencies, and means interposed in said path of travel for acoustically suppressing high frequency harmonics.

3. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds With the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for high frequencies, and a lplurality of acoustical filters interposed at spaced points in said path of travel for progressively suppressing high frequency harmonies.

4. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound Waves from said reeds to said outlet longer for low frequencies than for high frequencies, and a .plurality of baffles interposed at spaced points in said path of travel for progressively suppressing high frequency harmonics.

5. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet loacted near the highM-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for high frequencies, and baffle means for directing sound waves traveling in said path in a sinuous path.

6. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for high frequencies, and a plurality of Ibaffles interposed at spaced points in said path of travel and having relatively small openings through which said Waves pass.

7. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds with the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for high frequencies, and a plurality of baiflles interposed at spaced points in said path of travel, successive baiiies having staggered openings through which said waves pass.

8. An organ tone generator comprising a set of reeds of different pitch, and acoustical baille means interposed in the path of sound Waves from said reeds and constructed and arranged to absorb harmonic energy to a progressively increasing extent from the treble to the bass, thereby reducing the amplitude of the audible harmonies correspondingly.

9. An organ tone generator comprising a set of reeds of different pitch, and baffle means causing sound Waves from said reeds to follow a sinuous path, the number of said baffles and the resulting length of said path progressively increasing from the treble reeds to the bass reeds,

10. An organ tone generator comprising a set of reeds of different pitch, and acoustical filter means interposed in the path of travel of sound Waves from said reeds for suppressing undesirable reed harmonics, said filter means and reeds being disposed relative to each other so that a progressively greater number of said filter means are effective for the bass reeds than for the treble reeds.

1l. An organ tone generator comprising a casing having a sound outlet, a set of reeds arranged in a line of progressively higher-pitched reeds With the sound outlet located near the high-pitch end of the line, whereby the path of travel of sound waves from said reeds to said outlet is longer for low frequencies than for high frequencies, means interposed in said path of travel for reducing the amplitudes of reed harmonics to a progressively greater extent from the treble to the bass, and means for emitting sound Waves from said casing independently of said first named means.

12. In an electric organ, the combination of a plurality of reeds of different pitch, an electrical reproduction system having microphonic pick-up means, and means for reducing the energy of the sound waves reaching said pick-up means to a progressively greater extent as the pitch of the reeds decreases to suppress undesirable reed harmonies, said system including means for increasing the volume of tones of low frequency relative to tones of high frequency.

13. In an electric organ using reeds as tone generators and having an electrical reproduction system, acoustical means for suppressing undesired reed harmonics in the sound Waves from said reeds to a progressively greater extent from the treble to the bass, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said system also including means for suppressing harmonic frequencies whereby a pure flute-like quality of organ tone is produced.

14. In an electric organ using reeds as tone generators and having an electrical reproduction system, acoustical means for suppressing undesired reed harmonics in the sound waves from said reeds to a progressively greater extent from the treble to the bass, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies whereby a diapasonlike quality of organ tone is produced.

15. In an electric organ using reeds as tone generators and having an electrical reproduction system, acoustical means for suppressing undesired reed harmonics in the sound waves from said reeds to a progressively greater extent from the treble to the bass, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said system also including means for suppressing fundamentals whereby a string-like quality of organ tone is produced.

16. In an electric organ employing reeds as tone generators and having an electrical reproduction system, acoustical means for suppressing undesired reed harmonics in the sound Waves from said reeds to a progressively greater extent from the treble to the bass, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said. system also comprising a plurality of loud speakers adjusted to produce different qualities of tone corresponding to the stops of a pipe organ, such as flute, string and diapason.

17. In an electric organ employing reeds as tone generators and having an electrical reproduction system means for acoustically reducing the en ergy of sound Waves reaching said system to a progressively greater extent as the pitch of the reeds decreases to suppress undesirable reed harmonics, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said system also including means for Varying the ratio of harmonics to fundamentals whereby tones corresponding to a number of stops of a pipe organ can be obtained.

18. In an electric organ employing reeds as tone generators and having an electrical reproduction system, means for acoustically reducing the energy of sound Waves reaching said pick-up means to a progressively greater extent as the pitch of the reeds decreases to suppress undesirable reed harmonics, additional means adjustable to cause sound waves from said reeds to reach said pick-- up means directly, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said system also including means for varying the ratio of harmonics to fundamentals whereby tones corresponding to a number of stops of a pipe organ can be obtained.

19. In an electric organ employing reeds as tone generators and having an electrical reproduction system, means for acoustically reducing the energy of sound waves reaching said pick-up means tc a progressively greater extent as the pitch of the reeds decreases to suppress undesirable reed harmonics, additional means adjustable to cause sound Waves from said reeds to reach said pickup means directly, and means in said system for increasing the amplitudes of low frequencies relative to high frequencies, said system also including a plurality of loud speakers adjusted to pro-l duce different qualities of tone corresponding to the stops of a pipe organ, such as flute, string and diapason.

PHILIP HUBERT FROHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

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